Abstract
Sanicro 25 austenitic heat-resistant steel is expected to be used in superheaters and reheaters for ultra-supercritical power plants above 600 °C due to its excellent structural stability and high temperature mechanical properties. In this paper, the effects of Co and W on the structural stability, thermodynamic stability and mechanical properties of Sanicro 25 steel are analyzed by calculating the formation energy, binding energy, Gibbs free energy, elastic constant, Peierls stress and generalized stacking fault energy (GSFE) with first-principles calculation method. By calculating the formation energy, binding energy and Gibbs free energy, it concludes that alloying elements Co and W in Sanicro 25 steel can improve the structural stability and thermodynamic stability. It indicates that W and a small amount of Co can improve the plasticity and ductility of Sanicro 25 steel by calculating the bulk modulus (B), shear modulus (G), Young’s modulus (E), the B/G ratio, Poisson’s ratio and Peierls stress. It is found that when Co and W are far from the stacking fault region, it will promote the formation of partial dislocations and twins in the system, thereby improving its plastic deformation ability and mechanical properties.
Highlights
As a highly efficient and clean power generation technology, ultra-supercritical technology is the key development direction of coal-fired thermal power stations [1]
The calculation results of bulk modulus show that W will increase the compressive strength of the system, and the calculation results of Poisson’s ratio and generalized stacking fault energy show that W will increase the plastic deformation ability of the system, which is consistent with the experimental stress–strain curve results and our previous work [47]
We have revealed the effects of Co and W on structural stability and mechanical properties of Sanicro 25 austenitic heat-resistant steel through first principles calculations
Summary
As a highly efficient and clean power generation technology, ultra-supercritical technology is the key development direction of coal-fired thermal power stations [1]. In order to improve efficiency and reduce coal consumption, the 630–650 ◦ C ultra-supercritical unit is the important objective of the thermal power construction. Austenitic heat-resistant steels such as HR3C, which are used in 600 ◦ C ultra-supercritical units, are subjected to carbide precipitation and coarsening when operating under higher steam parameters. The structural stability is deteriorated, and the high-temperature mechanical properties and its service life will be seriously affected [2]. New materials that can withstand high temperature loads for a long time need to be developed in order to improve efficiency of the thermal power plants [3]. Sanicro 25 steel is the main candidate material for austenitic heat-resistant steel of 630–650 ◦ C ultra-supercritical boilers due to its high creep strength, oxidation resistance, structural stability and good processing ability [4]. By comparing the chemical composition and mechanical properties of HR3C [5] and Sanicro 25 [6] steel, it can be found that alloying elements such as Co and W play an Metals 2020, 10, 1051; doi:10.3390/met10081051 www.mdpi.com/journal/metals
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